The present invention relates to an electric power control apparatus, an electric power control method, and an electric power feeding system for controlling supply of electric power generated by a generating element.
As an environment protection measure, development of clean energy that does not emit carbon dioxide or polluting substances is desired. Among others, solar power generation and wind power generation have seen increasingly widespread use in recent years.
Particularly, use of solar power generating elements in general households is gradually becoming widespread due to the decrease in price and increase in generation efficiency of solar batteries (solar panels) that can be installed on rooftops of houses and the like.
Solar power generating elements have also become smaller in size, and sales of portable telephones equipped with a solar battery have been available.
A solar battery has characteristics different from those of constant voltage sources, such as dry-cell batteries, and has characteristics as a current source dependent on the voltage across its terminals.
Thus, in order to obtain a maximum output from a solar battery, the voltage of a load connected to the solar battery needs to be matched with the maximum operating point voltage of the solar battery.
In the current-voltage characteristics of a solar battery, there is only one maximum operating point (MPP: Maximum Power Point) where the electric power is at the maximum.
However, the current-voltage characteristics of a solar battery vary depending on the environment such as illuminance or temperature, so that the control for obtaining the maximum operating point voltage needs to be performed during operation of a device connected to the solar battery.
Such a control for obtaining the maximum operating point during operation of device is referred to as a MPPT (Maximum Power Point Tracking) control.
Many techniques for implementing the MPPT control have been proposed, and those techniques for the direct-current path can be roughly categorized into the following two types.
First type is a technique involving switching between series and parallel connections of a plurality of solar batteries (see Patent Document 1, for example).
Second type is a technique for obtaining the maximum operating point by controlling a switching type DC-DC converter (see Patent Document 2, for example).